KR20200022359A - Positive active material, method of manufacturing the same, and positive electrode and rechargeable lithium battery including the same - Google Patents

Abstract

Provided are a positive electrode active material, a manufacturing method thereof, and a positive electrode and a lithium secondary battery comprising the same. The positive electrode active material contains secondary particles having the average particle diameter of 15 to 25 μm, wherein the secondary particle includes lithium cobalt oxide comprising a plurality of primary particles having the average particle diameter of 2 to 10 μm. The pellet density of the positive electrode active material is greater than or equal to 3.80 g/cm^3.

Description

A positive electrode active material, a method of manufacturing the same, and a positive electrode and a lithium secondary battery including the same {POSITIVE ACTIVE MATERIAL, METHOD OF MANUFACTURING THE SAME, AND POSITIVE ELECTRODE AND RECHARGEABLE LITHIUM BATTERY INCLUDING THE SAME}

The present invention relates to a cathode active material, a method of manufacturing the same, and a cathode and a lithium secondary battery including the same.

A battery is a device that converts chemical energy generated during the electrochemical redox reaction of chemical substances into electrical energy. A primary battery that needs to be discarded when all the energy inside the battery is exhausted and a rechargeable battery that can be recharged many times Can be divided into: Among them, the secondary battery may be charged and discharged many times using reversible mutual conversion of chemical energy and electrical energy.

On the other hand, the recent development of the high-tech electronic industry is possible to reduce the size and weight of the electronic equipment is increasing the use of portable electronic devices. As a power source for such portable electronic devices, the necessity of a battery having a high energy density has been increased, and research on lithium secondary batteries has been actively conducted.

Such a lithium secondary battery includes a cathode including a cathode active material capable of intercalation and deintercalation of lithium, and an anode including a cathode active material capable of intercalating and deintercalating lithium. It is used to inject an electrolyte into a battery cell comprising a.

Among them, a lithium-containing compound capable of reversibly intercalating and deintercalating lithium is used as the cathode active material, and includes lithium-containing composite oxides such as lithium cobalt oxide, lithium manganese oxide, and lithium nickel oxide.

As the usage of the lithium secondary battery increases, the demand for a lithium secondary battery with improved size and weight, but improved efficiency and capacity, is increasing. Therefore, in order to provide a lithium secondary battery with improved efficiency and capacity, the need for an improved cathode active material is also increasing.

One embodiment provides a cathode active material having a high density and thermal stability and a method of manufacturing the same.

Another embodiment provides a positive electrode including the positive electrode active material.

Another embodiment provides a lithium secondary battery having improved efficiency and lifetime maintenance.

According to one embodiment includes a secondary particle having an average particle diameter of 15 ㎛ to 25 ㎛, the secondary particle comprises a lithium cobalt oxide comprising a plurality of primary particles having an average particle diameter of 2 ㎛ to 10 ㎛, A pellet active material having a pellet density of 3.80 g / cm ³ or more is provided.

According to another embodiment, the cobalt-containing compound is heat-treated at 900 ° C. or higher to form cobalt oxide including Co ₃ O ₄ and CoO, and the cobalt oxide is reacted with a lithium compound to form lithium cobalt oxide according to the embodiment. It provides a method for producing a positive electrode active material comprising a step of.

According to another embodiment, the current collector and the positive electrode active material layer, the positive electrode active material layer provides a positive electrode comprising the positive electrode active material described above.

According to another embodiment, a lithium secondary battery including the positive electrode, the negative electrode, and the electrolyte described above is provided.

The positive electrode active material may provide a high electrode density by having a high pellet density, thereby contributing to the improvement of electrochemical properties such as efficiency and lifetime maintenance of the lithium secondary battery.

1 is a view schematically showing a cross-section of a positive electrode active material according to an embodiment.
2 is a schematic diagram illustrating a rechargeable lithium battery according to one embodiment.
3 is a graph showing the results of X-ray diffraction (X-Ray Diffraction) analysis of each of the cobalt oxide generated during heat treatment at 800 ℃, 850 ℃ and 900 ℃.
Figure 4 is a graph showing the results of differential scanning calorimetry (DSC) evaluation of the positive electrode active material according to Example 1 and Comparative Example 1.

Hereinafter, exemplary embodiments will be described in detail with reference to the accompanying drawings. However, in describing the present disclosure, descriptions of already known functions or configurations will be omitted to clarify the gist of the present disclosure.

According to one embodiment, a cathode active material including lithium cobalt oxide is provided. The lithium cobalt oxide includes secondary particles having an average particle diameter of 15 μm to 25 μm, and the secondary particles include a plurality of primary particles having an average particle diameter of 2 μm to 10 μm, and the cathode active material is 3.80 g Pellet density of / cm ³ or more. As such, lithium cobalt oxide including secondary particles formed by aggregation of primary particles has a higher density than lithium cobalt oxide composed of single crystals without primary particles, and has excellent initial efficiency, rate characteristics, life retention rate, and thermal stability. Shows performance.

In this case, the average particle diameter is a value measured by inserting a plurality of particles into a particle size analyzer and measuring a particle diameter (D ₅₀ ) at ₅₀ % by volume in a cumulative size-distribution curve. Can be.

The positive electrode active material will be described with reference to FIG. 1. 1 is a view schematically showing a cross-section of a positive electrode active material according to an embodiment. Referring to FIG. 1, the positive electrode active material has an average particle size of 15 μm to 25 μm in which a plurality of primary particles 10 are aggregated by agglomeration of primary particles 20 having an average particle diameter of 2 μm to 10 μm. The primary particles 1 are formed.

The positive electrode active material may have a pellet density of 3.80 g / cm ³ or more, for example, 3.82 g / cm ³ or more. For example, the cathode active material may have a pellet density of 3.90 g / cm ³ or less, for example, 3.85 or less. It is possible to improve the electrode density in the above range.

Since the primary particles 10 are in close contact with each other, the secondary particles 1 may have an internal porosity of 10% or less. In addition, the internal pores of the secondary particles 1 may have a size of 5 nm or less, for example, 4 nm or less or 3 nm or less. The term "inner" herein refers to a region of 50 to 70 length%, for example, 60 length%, or an area within 2 μm of the outermost surface of the secondary particle, from the center to the outermost surface of the secondary particle. Refers to the rest of the area.

The ratio of the average particle diameter of the primary particle 20 and the secondary particle 1 is 1: 3 or more, 1: 4 or more, 1: 5 or more and 1:12 or less, for example 1:11 or less, 1 : 10 or less, 1: 9 or less, 1: 8 or less, or 1: 7 or less. In the above range, it is possible to improve the initial efficiency, the rate characteristic and the life retention rate of the positive electrode active material.

On the cross section cut to include the longest diameter of the secondary particles, there may be eight or more cross sections of the primary particles. That is, the number of primary particles present on the longest cross section of one secondary particle may be eight or more. As the number of primary particles increases, the initial efficiency rate characteristics and lifespan retention may be improved. In one embodiment, the cross section of the primary particles may be 20 or less, for example, 18 or less, 15 or less, or 12 or less. The number of cross-sections of these particles can be confirmed with a scanning electron microscope (SEM).

The c-axis lattice constant of the lithium cobalt oxide may satisfy the following range.

14.060 Å≤ c ≤ 14.069 Å

When the c-axis lattice constant of the lithium cobalt oxide satisfies the above range, the efficiency and lifetime maintenance rate of the lithium secondary battery manufactured by including the lithium cobalt oxide may be further improved. Lithium cobalt oxide corresponding to the layered compound has an excellent effect in terms of charging / discharging efficiency and lifetime maintenance rate as the c-axis length increases, thereby making lithium ions easily work.

The lithium cobalt oxide may further include an oxide containing at least one metal selected from Mn, Zn, Ti, and Co. For example, the oxide containing at least one metal may be coated on lithium cobalt oxide, and more specifically, the oxide may be coated on the surface of the lithium cobalt oxide in an island form.

The size of the oxide coated on the surface of the lithium cobalt oxide may be determined according to the size of the raw material, for example, may be 200 nm to 600 nm. These oxides are 0.5 parts by weight or more, for example 0.6 parts by weight, 0.7 parts by weight, 0.8 parts by weight or 1 part by weight and 5 parts by weight or less, for example 4 parts by weight, based on 100 parts by weight of lithium cobalt oxide. It may be included in an amount of less than or equal to 3 parts by weight. In this case, the initial efficiency and rate characteristics can be further improved.

In another embodiment, a cathode active material including a first lithium cobalt oxide and a second lithium cobalt oxide (small lithium cobalt oxide) having an average particle diameter of 2 μm to 10 μm is provided. The first lithium cobalt oxide is the lithium cobalt oxide (an alternative first lithium cobalt oxide) described above. As such, when the first lithium cobalt oxide and the small lithium cobalt oxide are mixed, the pellet density of the positive electrode active material and the electrode density of the positive electrode including the same may be further increased.

The first lithium cobalt oxide and the second lithium cobalt oxide may be included in a weight ratio of 6: 4 or more, for example 7: 3 or more and 9: 1 or less, for example 8: 2 or less. It is possible to further improve the pellet density and the electrode density of the positive electrode including the same in the above range.

At least one of the first lithium cobalt oxide and the second lithium cobalt oxide may further include an oxide containing at least one metal selected from Mn, Zn, Ti, and Co. For example, the oxide containing at least one metal may be coated on at least one surface of the first lithium cobalt oxide and the second lithium cobalt oxide. These oxides are 0.5 parts by weight or more, for example 0.6 parts by weight, 0.7 parts by weight, 0.8 parts by weight or 1 part by weight and 5 parts by weight or less, for example 4 parts by weight, based on 100 parts by weight of lithium cobalt oxide. Or up to 3 parts by weight. In this case, the initial efficiency and rate characteristics can be further improved.

The lithium cobalt oxide may be formed by reacting a cobalt oxide including CoO with a lithium compound. Cobalt oxide containing such CoO peaks in the 2 theta range of 40 degrees to 45 degrees in X-ray diffraction analysis.

The lithium cobalt oxide is prepared by heat treating a cobalt-containing compound at 900 ° C. or higher to form cobalt oxide including Co ₃ O ₄ and CoO, and reacting the cobalt oxide with a lithium compound to form lithium cobalt oxide. Can be.

The cobalt-containing compound may be Co (OH) ₂ , CoCO ₃ or a mixture thereof. When the cobalt-containing compound is heat treated at a temperature of 900 ° C. or higher, cobalt oxide including Co ₃ O ₄ and CoO is produced. When the cobalt oxide including the two oxide phases is reacted with a lithium compound, a plurality of primary particles may be gathered under the action of highly reactive CoO to produce a lithium cobalt oxide having a secondary particle shape.

The above-described lithium compound is, for example, lithium phosphate (Li ₃ PO ₄ ), lithium nitrate (LiNO ₃ ), lithium acetate (LiCH ₃ COOH), lithium carbonate (Li ₂ CO ₃ ), lithium hydroxide (LiOH) , Lithium dihydrogen phosphate (LiH ₂ PO ₄ ) or a combination thereof, but is not limited thereto.

The lithium compound may be added so that the molar ratio of lithium to cobalt is 0.8 to 1.0. When the molar ratio of lithium to cobalt is within the above range, the efficiency and lifetime maintenance rate of the lithium secondary battery including the prepared cathode active material may be improved. As such, a cobalt-containing compound is prepared by heat-treating a cobalt-containing compound at a temperature of 900 ° C. or higher, and when reacting the cobalt-containing compound at a temperature of 850 ° C., a cobalt oxide is prepared. A denser active material can be prepared than when reacted with a lithium compound.

Hereinafter, a positive electrode including the positive electrode active material will be described.

The positive electrode includes a current collector and a positive electrode active material layer formed on at least one surface of the current collector.

The current collector may use aluminum foil, but is not limited thereto.

The positive electrode active material layer includes the positive electrode active material, the binder, and the conductive material described above.

The binder adheres the positive electrode active materials well to each other, and also serves to adhere the positive electrode active materials to the current collector well, and representative examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, and polyvinyl chloride. , Carboxylated polyvinylchloride, polyvinylfluoride, polymers including ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene A rubber, an acrylated butadiene rubber, an epoxy resin, nylon, or the like may be used, but is not limited thereto.

The conductive material is used to impart conductivity to the electrode, and may be used as long as it is an electronic conductive material without causing chemical change, and examples thereof include natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, and the like. Carbon-based materials; Metal materials such as metal powder or metal fibers such as copper, nickel, aluminum and silver; Conductive polymer materials such as polyphenylene derivatives; Or a conductive material containing a mixture thereof.

The positive electrode may be prepared by mixing the positive electrode active material, the binder, and the conductive material in a solvent to prepare a positive electrode active material slurry, and applying the positive electrode active material slurry to a current collector.

N-methylpyrrolidone may be used as the solvent, but is not limited thereto.

At this time, the mixture density of the positive electrode is 4.00 g / cm ³ Or more, 4.03 g / cm ³ And at least 4.10 g / cm ³ or at 4.05 g / cm ³ It may be: When the mixture density of the positive electrode is in the above range, it is possible to obtain a positive electrode having excellent discharge capacity while preventing the problem of impregnation of the electrolyte solution, deterioration of high rate characteristics, fracture of the active material particles, or difficulty in enduring the current collector and breaking during the process. have.

The anode is not limited to the above enumerated forms but may be in any form other than the foregoing forms. In addition, the positive electrode may include, in addition to the positive electrode active material described above, at least one other technical feature such as the above-described positive electrode active material, composition, and particle size, and may further include a conventional positive electrode active material known in the art.

Hereinafter, a lithium secondary battery including the positive electrode described above will be described.

2 is a schematic view of a rechargeable lithium battery according to another embodiment. Referring to FIG. 2, the lithium secondary battery 100 includes a positive electrode 114, a negative electrode 112 positioned to face the positive electrode 114, and a separator 113 disposed between the positive electrode 114 and the negative electrode 112. And a battery cell including an electrolyte for a lithium secondary battery (not shown) impregnating the positive electrode 114, the negative electrode 112, and the separator 113, the battery container 120 containing the battery cell, and the battery container ( And a sealing member 140 for sealing 120.

The anode 114 may be the above-described anode.

The negative electrode 112 includes a current collector and a negative electrode active material layer formed on at least one surface of the current collector.

The current collector may be copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam (foam), copper foam, a polymer substrate coated with a conductive metal or a combination thereof.

The negative electrode active material layer includes a material capable of reversibly intercalating / deintercalating lithium ions, a lithium metal, an alloy of lithium metal, a material doped and undoped with lithium, or a transition metal oxide.

As a material capable of reversibly intercalating / deintercalating the lithium ions, any carbon-based negative electrode active material generally used in a lithium secondary battery may be used, and representative examples thereof include crystalline carbon, Amorphous carbons or these may be used together. Examples of the crystalline carbon may include graphite such as amorphous, plate, flake, spherical or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon may include soft carbon (soft carbon). Or hard carbon, mesophase pitch carbide, calcined coke, or the like.

Among them, especially when graphite is used, since there is no voltage change on the negative electrode side, it may be used together with the lithium cobalt oxide-based positive electrode active material to effectively produce a 3V class high capacity battery.

Examples of the alloy of the lithium metal include lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn. Alloys of the metals selected may be used.

Examples of materials that can be doped and undoped with lithium include Si, SiO _x (0 <x <2), and Si-Q alloys (wherein Q is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, and a rare earth element). And combinations thereof, and not Si, not Sn, Sn, SnO ₂ , or Sn-R alloys (wherein R is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, and a rare earth element). And an element selected from the group consisting of combinations thereof, not Sn, and at least one of these and SiO ₂ may be mixed and used. The elements Q and R include Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, One selected from the group consisting of S, Se, Te, Po, and a combination thereof can be used. In addition, at least one of these and SiO ₂ may be mixed and used.

The binder adheres the anode active material particles to each other well, and also serves to adhere the anode active material to the current collector well. As the binder, a water-insoluble binder, a water-soluble binder or a combination thereof can be used.

The water-insoluble binder includes polyvinyl chloride, carboxylated polyvinylchloride, polyvinyl fluoride, polymers including ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride , Polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

Examples of the water-soluble binder include styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, propylene and olefin copolymers having 2 to 8 carbon atoms, and (meth) acrylic acid and (meth) acrylic acid alkyl esters. Copolymers or combinations thereof.

When using the water-soluble binder as the negative electrode binder, it may further include a cellulose-based compound capable of imparting viscosity. As this cellulose type compound, carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or these alkali metal salts, etc. can be used in mixture of 1 or more types. Na, K or Li may be used as the alkali metal. The amount of the thickener used may be about 0.1 part by weight to about 3 parts by weight based on 100 parts by weight of the negative electrode active material.

As the conductive material, any one generally used in a lithium secondary battery may be used, and examples thereof include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber; Metal materials such as metal powder or metal fibers such as copper, nickel, aluminum and silver; Conductive polymers such as polyphenylene derivatives; Or a conductive material containing a mixture thereof.

The negative electrode may be prepared by a conventional process of preparing a negative electrode active material slurry by mixing a negative electrode active material, a binder, and optionally a conductive agent in a solvent, and then applying, drying, and rolling the negative electrode active material slurry on a current collector. Representative examples of the solvent may include, but are not limited to, N-methylpyrrolidone or water. Since such a negative electrode manufacturing method is well known in the art, a detailed description thereof will be omitted.

The electrolyte contains a non-aqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

As the non-aqueous organic solvent, a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, or aprotic solvent can be used. Examples of the carbonate solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and ethylene carbonate ( EC), propylene carbonate (PC), butylene carbonate (BC), etc. may be used, and the ester solvent may be methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate. , γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, and the like may be used. Dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used as the ether solvent, and cyclohexanone may be used as the ketone solvent. have. In addition, ethyl alcohol, isopropyl alcohol, and the like may be used as the alcohol solvent, and the aprotic solvent may be R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group. Amides such as nitrile dimethylformamide, dioxolane sulfolanes such as 1,3-dioxolane, and the like.

The non-aqueous organic solvent may be used alone or in combination of one or more, the mixing ratio in the case of using one or more mixed can be appropriately adjusted according to the desired battery performance, which is widely understood by those skilled in the art Can be.

Lithium salt is a substance that dissolves in an organic solvent and acts as a source of lithium ions in the battery to enable operation of the basic lithium secondary battery and to promote the movement of lithium ions between the positive electrode and the negative electrode. Representative examples of such lithium salts are LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN (SO ₂ C ₂ F ₅ ) ₂ , Li (CF ₃ SO ₂ ) ₂ N, LiN (SO ₃ C ₂ F ₅ ) ₂ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ), where x and y are natural numbers, for example Supporting one or more selected from the group consisting of LiCl, LiI and LiB (C ₂ O ₄ ) ₂ (lithium bis (oxalato) borate (LiBOB)); It is preferable to use the concentration of lithium salt within the range of about 0.1 M to about 2.0 M. When the concentration of the lithium salt is included in the above range, the electrolyte has an appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance. And lithium ions can move effectively.

The separator 113 separates the positive electrode 114 and the negative electrode 112 and provides a passage for moving lithium ions, and may be used as long as they are commonly used in lithium ion batteries. In other words, a low resistance to the ion migration of the electrolyte and excellent in the ability to hydrate the electrolyte can be used. For example, it is selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, and may be in a nonwoven or woven form. For example, a polyolefin-based polymer separator such as polyethylene or polypropylene is mainly used for a lithium ion battery, and a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength. Can be used as a structure.

The lithium secondary battery may be classified into a lithium ion battery, a lithium ion polymer battery, and a lithium polymer battery according to the type of separator and electrolyte used, and may be classified into a cylindrical shape, a square shape, a coin type, a pouch type, etc., Depending on the size, it can be divided into bulk type and thin film type. Since the structure and manufacturing method of these batteries are well known in the art, detailed description thereof will be omitted.

Hereinafter, the above-described aspects of the present invention will be described in more detail with reference to the following examples. However, the following examples are for illustrative purposes only and do not limit the scope of the present invention.

Example 1: Preparation of Positive Electrode Active Material

CoCO ₃ was heated to 900 ℃ at a temperature increase rate of 5 ℃ / min and maintained at 900 ℃ for 5 hours, and then subjected to a heat treatment under a condition that the temperature is reduced to 25 ℃ at a temperature reduction rate of 5 ℃ / min cobalt containing CoO phase An oxide (Co ₃ O ₄ ) was prepared.

Lithium carbonate (Li ₂ CO ₃ ) and the cobalt oxide were mixed by mixing Li: Co in a 1: 1 molar ratio to prepare a mixture.

The mixture was heated to 1050 ° C. at a temperature increase rate of 5 ° C./min and maintained at 1050 ° C. for 5 hours, and then subjected to heat treatment under a condition that the temperature was reduced to 25 ° C. at a temperature reduction rate of 5 ° C./min to form a plurality of primary particles. A LiCoO ₂ positive electrode active material including secondary particles including was prepared. The average particle diameter of the obtained secondary particles of LiCoO ₂ was 20 μm, and the average particle diameter of the primary particles was 3 μm.

Example 2: Preparation of Positive Electrode Active Material

LiCoO ₂ having an average particle diameter of 5 μm was prepared by heat treating lithium carbonate and cobalt oxide having an average particle size of 4 μm at 1050 ° C. in a molar ratio of 0.97: 1.

A positive electrode active material was prepared by mixing LiCoO ₂ (allergic lithium cobalt oxide) prepared according to Example 1 and LiCoO ₂ (smaller lithium cobalt oxide) obtained above at a 8: 2 weight ratio.

Example 3: Preparation of Positive Electrode Active Material

LiCoO ₂ with lithium carbonate and 4 μm of cobalt oxide was heat-treated at 1050 ° C. in a molar ratio of 0.97: 1 to prepare LiCoO ₂ having an average particle diameter of 5 μm.

A positive electrode active material was prepared by mixing LiCoO ₂ (allele lithium cobalt oxide) prepared according to Example 1 and the obtained LiCoO ₂ (small lithium cobalt oxide) in an 8: 2 weight ratio, followed by heat treatment at 950 ° C. with TiO ₂ . TiO ₂ was used in an amount of 1 part by weight based on 100 parts by weight of lithium cobalt oxide.

Comparative Example 1: Preparation of Positive Electrode Active Material

A mixture was prepared by mixing lithium hydroxide (LiOH) and Co (OH) ₂ in a 1: 1 molar ratio.

The mixture was heated to 400 ° C. at a temperature increase rate of 5 ° C./min and maintained at 400 ° C. for 5 hours, and then heat-treated under conditions such that temperature was reduced to 25 ° C. at a temperature reduction rate of 5 ° C./min. After re-mixing and uniformly dispersing, the second heat treatment was performed for 12 hours at 750 ℃ at the temperature and the temperature reduction temperature again to prepare a LiCoO ₂ cathode active material including a plurality of primary particles. The average particle diameter of the obtained primary particles of LiCoO ₂ was 1 μm, and the average particle diameter of the secondary particles was 10 μm.

Example 4: Fabrication of a Lithium Secondary Battery

A positive electrode active material slurry was prepared by mixing 96% by weight of the positive electrode active material according to Example 1, 2% by weight of Ketjen Black and 2% by weight of polyvinylidene fluoride in a N-methyl pyrrolidone solvent. The positive electrode active material slurry was coated, dried, and rolled on Al foil to prepare a positive electrode. A half cell was manufactured using the positive electrode, the lithium metal counter electrode and the electrolyte. The electrolyte used a mixed solvent (1: 1 volume ratio) of ethylene carbonate and dimethyl carbonate in which 1.0 M LiPF ₆ was dissolved.

Example 5 and Example 6: Fabrication of Lithium Secondary Battery

Instead of the positive electrode active material according to Example 1, the half cells according to Example 5 and Example 6 were prepared using the positive electrode active materials according to Examples 2 and 3, respectively.

Comparative Example 2: Fabrication of Lithium Secondary Battery

Instead of the positive electrode active material according to Example 1, each of the positive electrode active materials according to Comparative Example 1 was used to prepare a half cell according to Comparative Example 2.

Evaluation Example 1 X-ray Diffraction Analysis of Cobalt Oxide According to Heat Treatment Temperature

X-ray diffraction (X-ray diffraction) analysis of cobalt oxide produced by heat treatment of CoCO ₃ at 800 ° C, 850 ° C, and 900 ° C. Cu Kα ray was used as the light source, and measured at a range of 10 ° ≦ 2θ ≦ 80 ° and a scan rate of 1 ° / min. The result is shown in FIG. Referring to FIG. 3, it can be seen that X-ray diffraction peaks of cobalt oxide having a CoO structure were observed only in cobalt oxide heat-treated at 900 ° C. or higher.

Evaluation Example 2: X-ray Diffraction Diffraction Analysis of Positive Electrode Active Material

X-ray diffraction patterns were measured using CuKα rays of the positive electrode active materials according to Example 1 and Comparative Example 1, and the results are shown in Table 1.

a (Å) c (Å) c / a Example 1 2.816 (5) 14.063 (3) 4.995 Comparative Example 1 2.817 (5) 14.058 (6) 4.990

In Table 1, the numbers in parentheses indicate the standard deviation values. In Table 1 it can be seen that the c-axis lattice constant value of the positive electrode active material according to Example 1 is larger than the positive electrode active material according to Comparative Example 1.

Evaluation Example 3 Pellet Density of Positive Electrode Active Material

The pellet densities of the positive electrode active materials prepared according to Examples 1 to 3 and Comparative Example 1 were evaluated. The pellet density was measured and recorded within the range of 3.0000 g (error range ± 0.0004 g) of the positive electrode active material. The positive electrode active material was held at a presser 4 ton for 30 seconds using a 13 mm size KBr Pellet Die to measure the decrease in height and then the weight per volume. The measurement results of the positive electrode active materials of Example 1, Example 3, and Comparative Example 1 are shown in Table 2 below.

Evaluation Example 4 Mixing Density of the Positive Electrode

The mixture density of the positive electrode active materials prepared according to Examples 1 to 3 and Comparative Example 1 was evaluated. The mixture density is 97% by weight of the positive electrode active material, 1.5% by weight of Ketjen Black and 1.5% by weight of the binder in a N-methyl pyrrolidone solvent to prepare a positive electrode active material slurry and coating the positive electrode active material slurry on Al foil (substrate), The maximum mixture density reflecting the mixture density and substrate stress at normal pressure was measured by rolling for each drying and pressing pressure. The measurement results of the positive electrode active materials of Example 1, Example 3, and Comparative Example 1 are shown in Table 2 below.

Sample Pellet Density (g / cm ³ ) Mixture density (g / cm ³ ) Example 1 3.80 4.03 Example 3 3.84 4.10 Comparative Example 1 3.77 3.98

Referring to Table 2, it can be seen that the pellet density of the positive electrode active material according to Examples 1 and 3 and the mixture density of the positive electrode including the same are improved compared to the positive electrode active material according to Comparative Example 1.

Evaluation Example 5: Thermal Stability of Positive Electrode Active Material

The thermal stability of the positive electrode active material prepared according to Examples 1 to 3 and Comparative Example 1 is evaluated. After charging the half cells according to Examples 4 to 6 and Comparative Example 2 including the positive electrode active material prepared according to Examples 1 to 3 and Comparative Example 1 to 4.5V at 0.1C to recover the positive electrode active material by disassembling the battery. Post thermal differential calorimetry (DSC) is used to assess thermal stability. The results of DSC evaluation of the positive electrode active material according to Example 1 and Comparative Example 1 are shown in Table 3 and FIG. 4. Figure 4 is a graph showing the results of differential scanning calorimetry (DSC) evaluation of the positive electrode active material according to Example 1 and Comparative Example 1.

onset
(℃) Max. temp. (℃) Total J (J / g) Example 1 220 316 2353 Comparative Example 1 190 302 2575

Referring to Table 3 and FIG. 4, it can be seen that the onset temperature of the cathode active material according to Example 1 is higher than the onset temperature of the cathode active material according to Comparative Example 1, the maximum exothermic temperature is also high, and the total amount of heat is small. From this, it can be seen that the cathode active material according to Example 1 is superior in thermal stability to the cathode active material according to Comparative Example 1.

Evaluation Example 6: Electrochemical Characteristics of Lithium Secondary Battery

The half-cells prepared according to Examples 4 to 6 and Comparative Example 2 were once charged and discharged at 0.1C to evaluate initial charge and discharge efficiency. After charging and discharging the half cell at 0.1 C once, charging at 0.1 C for 4.5 V cut-off and charging 0.05 C cut-off under constant voltage conditions, then discharging at 1.0 C under constant current conditions and 3.0 V cut-off conditions 1C discharge capacity was measured. The rate characteristics were evaluated by obtaining the 1C discharge capacity / 0.1C discharge capacity. The half cell was charged at 1.0 C (1.0 C = 160 mAh / g) under constant current conditions at room temperature (25 ° C.) and charged at 0.05 C cut-off under constant voltage conditions and then charged at 1.0 C under constant current conditions. , Charging and discharging discharged under 3.0V cut-off conditions were performed 50 times to evaluate the life retention rate. The results are shown in Table 4 below.

Initial capacity
(0.1C, mAh / g) Initial efficiency
(0.1C,%) Properties
(1C / 0.1C) Longevity
(50 cycle) Example 4 199.62 97.02 92.66% 91.95% Example 5 198.52 96.83 93.14% 92.66% Example 6 199.98 97.23 93.47% 92.87% Comparative Example 2 197.75 96.50 91.80% 90.30%

Referring to Table 4, it can be seen that the lithium secondary batteries according to Examples 4 to 6 are superior in initial capacity and initial efficiency as well as excellent in rate characteristics and lifetime retention than the lithium secondary batteries according to Comparative Example 2. Can be.

While specific embodiments of the invention have been described and illustrated above, it is to be understood that the invention is not limited to the described embodiments, and that various modifications and changes can be made without departing from the spirit and scope of the invention. It is self-evident to those who have. Therefore, such modifications or variations are not to be understood individually from the technical spirit or point of view of the present invention, the modified embodiments will belong to the claims of the present invention.

DESCRIPTION OF SYMBOLS 1 Secondary particle 10 Multiple primary particle 20 Primary particle
100: lithium secondary battery 112: negative electrode
113: separator 114: positive electrode
120: battery container 140: sealing member

Claims (16)

Including secondary particles having an average particle diameter of 15 μm to 25 μm,
The secondary particles include a lithium cobalt oxide containing a plurality of primary particles having an average particle diameter of 2 ㎛ to 10 ㎛,
The pellet density of the positive electrode active material is 3.80 g / cm ³ or more,
Cathode active material for lithium secondary battery. The method of claim 1,
The pellet density of the positive electrode active material is 3.80 g / cm ³ to 3.85 g / cm ³ ,
Cathode active material for lithium secondary battery. The method of claim 1,
The secondary particles have an internal porosity of 10% or less,
Cathode active material for lithium secondary battery. The method of claim 1,
Internal pores of the secondary particles have a size of 5 nm or less,
Cathode active material for lithium secondary battery. The method of claim 1,
The ratio of the average particle diameter of the primary particles and the secondary particles is 1: 3 to 1:12,
Cathode active material for lithium secondary battery. The method of claim 1,
On a cross section cut to include the longest diameter of the secondary particles, the primary particles have a cross section of 8 or more,
Cathode active material for lithium secondary battery. The method of claim 1,
The positive electrode active material for a lithium secondary battery, wherein the c-axis lattice constant c of the lithium cobalt oxide satisfies the following range:
14.060 Å≤ c ≤ 14.069 Å. The method of claim 1,
The lithium cobalt oxide further includes an oxide containing at least one metal selected from Mn, Zn, Ti, and Co,
Cathode active material for lithium secondary battery. The method of claim 1,
The positive electrode active material further includes a second lithium cobalt oxide,
The average particle diameter of the second lithium cobalt oxide is 2 ㎛ to 10 ㎛,
Cathode active material for lithium secondary battery. The method of claim 9,
The first lithium cobalt oxide and the second lithium cobalt oxide are included in the weight ratio of 6: 4 to 9: 1,
Cathode active material for lithium secondary battery. The method of claim 9,
At least one of the first lithium cobalt oxide and the second lithium cobalt oxide further includes an oxide containing at least one metal selected from Mn, Zn, Ti, and Co,
Cathode active material for lithium secondary battery. The cobalt-containing compound is heat-treated at 900 ° C. or higher to form a cobalt oxide including Co ₃ O ₄ and CoO,
Reacting the cobalt oxide with a lithium compound to produce lithium cobalt oxide,
The manufacturing method of the positive electrode active material for lithium secondary batteries of Claim 1 containing the process. The method of claim 12,
The said lithium compound is added so that the molar ratio of lithium with respect to cobalt may be 0.8-1.0, The manufacturing method of the positive electrode active material for lithium secondary batteries. Current collector; And
It includes a positive electrode active material layer,
The positive electrode active material layer,
A positive electrode for a lithium secondary battery comprising the positive electrode active material according to any one of claims 1 to 11 or the positive electrode active material prepared by the manufacturing method according to claim 12. The method of claim 14,
Electrode density of the positive electrode is a lithium secondary battery positive electrode of 4 g / cm ³ or more. An anode according to claim 14;
cathode; And
Lithium secondary battery comprising an electrolyte.

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